Purified titanium oxide with novel morphologies upon spark anodization of Ti alloys in mixed H2SO4/H3PO4 electrolytes.

The spark anodization behavior of alpha/beta Ti6Al4V and Ti6Al7Nb alloys and of alpha c.p. Ti in H2SO4, H3PO4, and mixtures of these acids was studied. Chemical depth profiling revealed oxides purified with respect to the substrate alloying elements. This was particularly pronounced on Ti alloys spark anodized in H2SO4/H3PO4 mixtures, the Al content decreasing continuously towards the surface, and V and Nb hardly detectable in the outermost 200 nm. The incorporation of S was significantly reduced in mixed electrolytes, while about 8 at-% P was present. A novel oxide morphology with "worm-like" features in the micrometer range, very different from well-known nano/microporous oxides, was found in mixed electrolytes under suitable conditions. Similar but more porous-like morphologies were formed on Ti. Simple alpha/beta substrate microstructural considerations cannot explain the morphological and chemical observations. Raman spectroscopy indicated the presence of mixed anatase, rutile, and brookite phase on anodized Ti alloys. Bond strengths of 34 MPa for worm-like and 40-50 MPa for nano/microporous morphologies as well as excellent abrasion behavior were found. The compatibility of grit-blasting with the spark anodization process for creating multitopography surfaces was demonstrated. Neither the observed chemical effects, nor the observed particular morphology or the presence of brookite have been reported before.

Differential regulation of osteoblasts by substrate microstructural features.

Microtextured titanium implant surfaces enhance bone formation in vivo and osteoblast phenotypic expression in vitro, but the mechanisms are not understood. To determine the roles of specific microarchitectural features in modulating osteoblast behavior, we used Ti surfaces prepared by electrochemical micromachining as substrates for MG63 osteoblast-like cell culture. Cell response was compared to tissue culture plastic, a sand-blasted with large grit and acid-etched surface with defined mixed microtopography (SLA), polished Ti surfaces, and polished surfaces electrochemically machined through a photoresist pattern to produce cavities with 100, 30 and 10 microm diameters arranged so that the ratio of the microscopic-scale area of the cavities versus the microscopic-scale area of the flat region between the cavities was equal to 1 or 6. Microstructured disks were acid-etched, producing overall sub-micron-scale roughness (Ra=0.7 microm). Cell number, differentiation (alkaline phosphatase; osteocalcin) and local factor levels (TGF-beta1; PGE(2)) varied with microarchitecture. 100 microm cavities favored osteoblast attachment and growth, the sub-micron-scale etch enhanced differentiation and TGF-beta1 production, whereas PGE(2) depended on cavity dimensions but not the sub-micron-scale roughness.

Time-dependent morphology and adhesion of osteoblastic cells on titanium model surfaces featuring scale-resolved topography.

The role of micrometer and submicrometer surface roughness on the interaction of cells with titanium model surfaces of well-defined topography was investigated using human bone-derived cells (MG63 cells). The early phase of interactions was studied using a kinetic morphological analysis of adhesion, spreading and proliferation of the cells. By SEM and double immunofluorescent labeling of vinculin and actin, it was found that the cells responded to nanoscale roughness by a higher cell thickness and a delayed apparition of the focal contacts. A singular behavior was observed on nanoporous oxide surfaces, where the cells were more spread and displayed longer and more numerous filopods. On electrochemically microstructured surfaces with hemispherical cavities, arranged in a hexagonal pattern, the MG63 cells were able to go inside, adhere and proliferate in cavities of 30 or 100 microm in diameter, whereas they did not recognize the 10 microm diameter cavities. Cells adopted a 3D shape when attaching inside the 30 microm diameter cavities. Condensation of actin cytoskeleton correlated with vinculin-positive focal contacts on cavity edges were observed on all microstructured surfaces. Nanotopography on surfaces with 30 microm diameter cavities had little effect on cell morphology compared to flat surfaces with same nanostructure, but cell proliferation exhibited a marked synergistic effect of microscale and nanoscale topography.